The present invention relates generally to electrostatic spraying devices for spraying powdered material on an article.
The invention concerns two types of electrostatic spraying devices. The first type has an axially extending body with a powder channel extending axially through the spraying device and a spraying opening at a downstream end of the spraying device. A rod-like support which lies on the axis of the device extends from the spraying opening for some distance into the powder channel.
Extending along the axis, beyond the spraying opening and coupled to the support is a powder deflection device. The deflection device receives a supply of gas from a gas channel which is provided within the spraying device body. The gas is guided by the powder deflection device to flow in a generally radial direction so as to form a gas wall which extends transversely to the axis of the spraying device. The effect of the gas wall is to further pulverize the powdered material and to mix and disperse it into a cloud of the material. At least one electrode, which is connected to a high voltage, is provided in the spraying device for electrostatically charging the powdered material.
The second type of spraying device is similar to the first type, except that the powder deflection device comprises a baffle against which the powdered material issuing from the spraying opening impinges to transform the axially flowing stream of particles into a cloud of powder.
Various electrostatic spraying devices are known. Japanese patent application No. 54-80 06, published under No. 55-99 361(A), as well as its Abstract which appears in "Patent Abstract of Japan," Oct. 29, 1980, Vol. 4, No. 155 describes a powder deflection device formed of a thickened, tear-shaped extension of an axial support which extends in the spraying device. A plurality of openings in the powder deflection device are arranged, star-like, around the thickened tear-shaped section. The openings are inclined forwardly in the direction of flow of the stream of powder and produce a gas wall which extends generally transversely to the stream of powder. The stream of powder is thereby converted into a cloud of powder.
German Application DE-OS No. 23 12 363 shows an electrostatic spraying device having a centrally located and axially extending support from which a pneumatically operable powder deflection device extends. An annular electrode located downstream of the spraying opening forms a short channel section which is part of the outer face of the powder channel and which serves to electrostatically charge the powdered material.
U.S. Pat. No. 4,289,278 discusses the feasibility of providing an electrode which extends axially within the powder channel and downstream of the spraying opening, generally at the axis or at the radial center of the device. Moving gas around the electrode to assure that particles of powder are not deposited on the electrode is also shown. Such an electrode can be located directly within the stream of powder or in a gas channel which leads into the powder channel.
EPO Publication No. 0 123 964 Al relating to European patent application No. 84 103 84.7 illustrates a spraying device with a pneumatically operable powder deflection device which is located downstream, outside, and beyond the spraying opening of the spraying device. The powder deflection device is supported by a support of the spraying device which extends axially through the spraying opening into the powder channel. The powder deflection device produces a gas wall which flows out of a substantially radial annular slot which is slightly inclined forwardly in the downstream direction of the powder. The annular slot is defined by a front face of the support and a disk located forwardly of the front face. The disk is a semiconductor electrode which is connected to a high voltage.
German Application DE-OS No. 19 32 387 describes an electrostatic spraying device in which an electrode is arranged centrally in an axially extending channel and directly upstream of the spraying opening. Two annular slits are disposed axially behind one another in the outer face of the channel. The annular slits coaxially surround the electrode. Air is supplied through the first annular slot nozzle while a colored liquid which is supplied from the second annular slit nozzle flows against the electrode.
German Patent No. 25 39 27, which substantially corresponds to US. Pat. No. 3,940,061, illustrates an electrode which is moved about by a flow of air and which is located at the center of the spraying opening of an electrostatic spraying device.